√3sina-sin(π/2-2a)/cos(π+a).cosa=1
√3sina-cos2a/(-cosa)*cosa=1
√3sina+cos2a-1=0
√3sina-2sin^2a=0
(√3-2sina)sina=0
sina=0或sina= √3/2
a=π/3还有3π/2,sin120=根号3/2a=π/3 ,a=2π/3